1. Field of the Invention
The present invention relates to optical prism design technology and more particularly, to a shaped optical prism structure, which is based on the principle that lights will fully reflected when their refraction angle/incident angle is greater than the critical angle of the medium, and practical for use in different lighting fixtures, such as street light or wall lamp, for enabling lamp emitted light to be projected onto a predetermined illumination area after having been fully reflected multiple times.
2. Description of the Related Art
A street or park light, as shown in FIG. 3, generally comprises a lamp post 301, a lamp 302 fixedly located on the top side of the lamp post 301 and holding a light source 303 therein and a light-permeable lampshade 304 surrounding the light-outgoing side of the lamp 302 for letting light rays to go in all directions. As the light-permeable lampshade 304 enables light rays to go in all directions, this design of street or park light achieves less road illumination effect and can cause light pollution.
To avoid light pollution and glaze, an improved design of street light was created, as shown in FIG. 4. According to this design, the street light comprises a lamp post 401, a lamp 402 fixedly mounted on the top side of the lamp post 401 and holding therein a light source 403 having an upward light-outgoing surface, and a reflective panel 404 mounted on the lamp post 401 and suspending above the lamp 402 for reflecting emitted light toward the ground. This design of street light is still not satisfactory in function. The illumination range of this design of street light is limited. Further, after a long use, the reflective panel 404 tends to be covered with dust, lowering its reflective performance.
U.S. Pat. No. 6,807,369 and U.S. Pat. No. 7,273,305 pertain to the same field relative to the present invention. According to the design of U.S. Pat. No. 6,807,369, as shown in FIG. 1, the illumination device includes a light distribution module consisting of a first optical member 2 and a second optical member 1. The first optical member 2 comprises a rounded incident surface 2a and two vertical incident surfaces 2b;2b′ located on the bottom side thereof, two sloping reflective surfaces 2c;2c′ located on the periphery, and a convex light-outgoing surface 2d located on the top side thereof. The first optical member 2 is adapted for focusing 360 o light rays emitted by a linear light source 3 onto an illumination area within the range of 90°. The second optical member 1 has a bottom incident surface provided with multiple recesses and a planar light-outgoing surface located on the top side thereof. The second optical member 1 is adapted for controlling distribution of light. After having been fully reflected once, light rays are refracted out of the light distribution module to illuminate a front area. This optical design is adapted for use in a lighting fixture for photographic apparatus, not suitable for street or part illumination.
U.S. Pat. No. 7,273,305 discloses a lighting device 14. The lighting device 14 comprises a plurality of incident surfaces 25 made in the form of a rounded recess and located on the bottom side thereof around a set of light sources 12, a plurality of arched reflective surfaces 36 at the periphery, and a planar light-outgoing surface 38 located on the top side. Light rays 34 emitted by the light sources 12 are fully reflected by the arched reflective surfaces 36 and then refracted out of the lighting device 14 by the planar light-outgoing surface 38. This design is especially suitable for automotive center-high-mounted-stop-light (CHMSL) and brake light applications.